Reaction products of a difunctional compound and an organo titanate

ABSTRACT

Reaction products of a difunctional compound and an organotitanate, process for the preparation thereof and the use of these reaction products as crosslinking agents in the preparation of cured products based on alkylene-alkyl acrylate copolymers. The cured products are especially useful as protective coatings about wires and cables.

This application is a division of application Ser. No. 402,981, filed Aug. 3, 1982, now U.S. Pat. No. 4,444,957 which in turn is a continuation-in-part of application Ser. No. 106,502, filed Dec. 26, 1979, now U.S. Pat. No. 4,351,926, granted Sept. 28, 1982.

SUMMARY OF THE INVENTION

The present invention relates to reaction products of a difunctional compound and an organo titanate and process for the preparation thereof. The reaction products are useful as crosslinking agents in the preparation of cured products based on alkylene-alkyl acrylate copolymers. The cured products are especially useful as protective coatings about wires or cables.

BACKGROUND OF THE INVENTION

Prior methods of curing, i.e. crosslinking, polymers include use of various peroxides. A mixture of polymer and a small amount of peroxide is prepared, and the mixture is cured with heat. The difficulty with this method is that the curing process generates volatile compounds which vaporize at the curing temperature if the pressure is low. Hence, unless the curing is carried out at high pressure in expensive pressure chambers, the cured polymer will have voids caused by the vaporized material.

Another method of curing polymers is by use of electron beams. However, this mwethod requires expensive electron beam generating apparatus, and is unacceptably slow if the polymer being cured is thick.

U.S. Pat. No. 3,646,155 (Scott) discloses a water curable polymer. However, its manufacturer recommends use of relatively expensive silane compounds and intimate contact with water to effect crosslinking.

OBJECTS

Accordingly, it is an object of this invention to provide crosslinking agents for crosslinking alkylene-alkyl acrylate copolymers without the use of high pressure during cure.

It is another object of this invention to provide heat-cured alktylene-alkyl acrylate copolymers which are useful as coatings about wire or cable.

It is a further object of this invention to provide a process for the preparation of curable alkylene-alkyl acrylate copolymers without the use of silane compounds as curing agents.

DESCRIPTION OF THE INVENTION

These and other objects are accomplished by the present invention, one aspect of which comprises preparing a crosslinking agent by reacting a mixture containing:

(a) a difunctional compound having the formula:

    R.sub.1 --R.sub.2 --R.sub.3

wherein R₁ and R₃ are independently selected from the group consisting of --OH, --SH, ##STR1## wherein R₄ is C₁ to C₂₀ hydrocarbon; R₂ is a divalent organic radical terminated with other than aryl and

(b) from 5 to 100 parts by weight, based on 100 parts by weight of the difunctional compound, of an organo titanate.

In carrying out the reaction, temperatures on the order of 25° C. to 250° C. are conveniently employed.

Also, it is preferred to remove volatile material from the reaction product prior to use.

The reaction product or adduct produced, as previously stated, is useful as a crosslinking agent for alkylene-alkyl acrylate copolymers. The reaction product can be used per se or in admixture with an inert or non-reactive polymer which serves as a carrier.

Another aspect of the present invention relates to a process for preparing a heat curable alkylene-alkyl acrylate copolymer by reacting a mixture containing:

(a) a difunctional compound having the formula:

    R.sub.1 --R.sub.2 --R.sub.3

wherein R₁ and R₃ are independently selected from the group consisting of --OH, --SH, ##STR2## wherein R₄ is C₁ to C₂₀ hydrocarbon; R₂ is a divalent organic radical terminated with other than aryl and

from 5 to 1,000 parts by weight, based on 100 parts by weight of the difunctional compound, of an organo titanate at a temperature of from 25° C. to 250° C. to produce a reaction product,

(b) removing volatile material from the step (a) reaction product, and

(c) reacting the devolatilized reaction product with an alkylene-alkyl acrylate copolymer.

In another aspect of the present invention, a heat-curable alkylene-alkyl acrylate copolymer is prepared by reacting a mixture containing:

(a) an alkylene-alkyl acrylate copolymer,

(b) from 0 to 10 parts by weight, based on 100 parts by weight of the copolymer, of a difunctional compound having the formula:

    R.sub.1 --R.sub.2 --R.sub.3

wherein R₁ and R₃ are independently selected from the group consisting of --OH, --SH, ##STR3## wherein R₄ is C₁ to C₂₀ hydrocarbon; R₂ is a divalent organic radical terminated with other than aryl, and

(c) from 0.1 to 10 parts by weight, based on 100 parts by weight of copolymer, of a titanium chelate.

Curing of a heat-curable copolymer so produced, requires curing at elevated pressure, generally on the order of about 5 to about 50 psig in order that a void free polymer be obtained. Silane compounds, however, are not required.

Crosslinked products of the heat-curable copolymers contain repeating units of:

(a) alpha olefin units having the formula: ##STR4## wherein B is selected from the group consisting of hydrogen, C₁ to C₁₆ alkyl, C₆ to C₁₂ aryl, C₇ to C₁₆ alkaryl or combinations thereof, said alpha olefin units being present in the copolymer to the extent of at least 22 weight percent;

(b) crosslinked bridges of the formula: ##STR5## wherein C₁ is a carbon atom in the polymer chain, and R₂ is a divalent organic radical terminated with other than aryl.

The present invention is predicated upon the discovery that when alkylene-alkyl acrylate copolymer, difunctional compound, and certain titanium compound are reacted, there results a heat-curable polymer that does not necessarily require high pressure curing. While not wishing to be bound by any particular theory, it is believed that the cured polymer is formed as follows:

First, the titanate, typically a titanate ester, reacts with the difunctional compound to form a different titanate ester and volatile alcohol or ester. The alcohol or ester may be removed during the initial compounding step before curing and even before the polymer is molded or extruded to its final form. The structures of the esters so formed are dependent on several factors including the relative mole ratio of titanate to difunctional compound, reaction time and temperature. Upon the application of heat, the esters formed in the first reaction cure the polymer. Overall, reactions occurring may be summarized as follows for typical reactants in accordance with the invention: ##STR6##

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in terms of its key ingredients: copolymer, difunctional compound and titanate. Then the preferred means of processing the ingredients into crosslinkable polymers will be discussed.

THE ALKYLENE-ALKYL ACRYLATE COPOLYMER

As used throughout the present specification and claims, the term "alkylene-alkyl acrylate copolymer" is intended to mean a copolymer formed by copolymerizing

(a) olefin monomer having the formula: ##STR7## wherein B is hydrogen, C₁ to C₁₆ alkyl, aryl, alkaryl or combinations thereof, including but not limited to ethylene, propylene, higher alpha olefins, and styrene.

(b) alkyl arcylate monomer having the formula: ##STR8## wherein B' is hydrogen or C₁ to C₅ alkyl and B" is C₁ to C₁₈ alkyl.

The preferred alkylene-alkyl acrylate copolymer is ethylene-ethyl acrylate copolymer containing from about 1 to about 50 percent by weight ethyl acrylate. The most preferred copolymer is ethylene-ethyl acrylate copolymer containing from 2 to about 20 percent by weight ethyl acrylate.

The alkylene-alkyl acrylate copolymers generally have a density (ASTM 1505 test procedure with conditioning as in ASTM D-148-72) of about 0.90 to 0.96 and a melt index (ASTM D-1238 at 44 psi. tested pressure) of about 0.5 to 500 decigrams per minute.

Another preferred alkylene-alkyl acrylate copolymer is ethylene-butyl acrylate copolymer. Other monomers may be copolymerized with the olefin and alkyl acrylate. Hence, ethylene-alkyl acrylate-acrylic acid terpolymers are also acceptable and included in the definition of "alkylene-alkyl acrylate" as used in the present specification and claims.

THE DIFUNCTIONAL COMPOUNDS

The difunctional compounds are of the general formula:

    R.sub.1 --R.sub.2 --R.sub.3

wherein R₁ and R₃ are independently selected from the group consisting of --OH,--SH, ##STR9## wherein R₄ is C₁ to C₂₀ hydrocarbon. R₂ is a divalent organic radical terminated with other than aryl. Hence R₂ includes, but is not limited to C₂ -C₂₀ unsubstituted hydrocarbon, including alkyl, cycloalkyl, and alkaryl, C₂ -C₂₀ hydrocarbon partially substituted by halogen, or ##STR10## wherein m is an integer of 0 to 20, Y¹ to Y^(m+2) are independently selected from divalent C₂ -C₂₀ hydrocarbon, and C₂ -C₂₀ hydrocarbon partially substituted by halogen; and X¹ to X^(m+1) are independently selected from the group consisting of O, S, N, Z, and combinations thereof wherein Z is C₁ to C₂₀ alkyl.

Preferred difunctional compounds are: ##STR11## wherein d is an integer of 1 to 4 dibromoneopentyl glycol; and ##STR12## wherein e is an integer of 2 to 20; and f and g are integers of 0 to 18.

However, difunctional compounds wherein R₂ is terminated by aryl are not acceptable. Hence bisphenol-A, having the formula: ##STR13## is unacceptable, because its R₂ ##STR14## terminates with aryl.

THE ORGANOTITANATE

As used throughout the present specification and claims, the term "organotitanate" is intended to mean a compound of the formula: ##STR15## wherein R₇, R₈, R₉ and R₁₀ are independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, alkaryl, aralkyl, of 1 to 20 carbon atoms, lactyl and acyl of the formula ##STR16## wherein R₁₁ is C₁ to C₂₀ alkyl and b is an integer of from 1 to 100, with the proviso that not all of R₇, R₈, R₉ and R₁₀ be H, acyl, or alkaryl. These organo titanates are commercially available materials and are prepared according to the procedures as set forth in U.S. Pat. No. 2,984,641, the disclosure of which is incorporated herein by reference.

Preferred titanates are: tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraoctyl titanate, tetra stearyl titanate, isopropyl tri (lauryl-myristyl) titanate, and combinations thereof.

The most preferred organo titanates are tetrabutyl titanate and tetraisopropyl titanate.

THE TITANIUM CHELATES

One aspect of the invention uses titanium chelates. As used throughout the present specification and claims, the term "titanium chelate" is intended to mean an organo titanium compound wherein titanium ion is held by coordination bonds. Such titanium chelates are described in the booklet Versatile TYZOR® Organic Titanates, published by E. I. duPont de Nemours & Co., Inc., Wilmington, Delaware. Preferred titanium chelates are: titanium actyl acetonate, lactic acid titanium chelate, triethanolamine titanium chelate, tetraoctylene glycol titanium chelate, and mixtures thereof.

ADJUVANTS

Adjuvants such as fillers including carbon black, clay, magnesium silicate, calcium carbonate, silicas, aluminum hydroxide, calcium silicate, etc. may be used with the heat curable polymers of this invention in amounts sufficient to produce the intended effect.

The copolymer may be rendered flame retardant by use of known halogen-containing flame retardant additives, preferably in admixture with an organic or inorganic antimony compound, e.g. antimony oxide.

Additionally, it is believed that compositions containing the present polymer, halogen-containing flame retardant and at least one of CaO,CaCO₃, Ca(OH)₂, CaSO₄, MgO, MgCO₃, Mg(OH)₂, and MgSO₄ would have advantageous properties. The halogen-containing flame retardants include decabromodiphenyl oxide, chlorinated polyethylene, polyvinyl chloride, halogenated paraffin waxes, and the reaction product of tetrabromophthalic acid anhydride and ethylene diamine.

PROCESSING THE INGREDIENTS

Three methods of processing the ingredients are currently known.

(1) The copolymer, difunctional compound and titanate are mixed and heated to a temperature of between the melting temperature of the copolymer and about 200° C. This is preferably accomplished by pre-blending copolymer and difunctional compound in a blender such as a Brabender or Banbury. The difunctional compound is blended with the copolymer in the amount of 0.1 to 10 parts by weight of difunctional compound based on 100 parts by weight of copolymer. Next, the blend is fed to an extruder, and 0.1 to 10 parts by weight of organo titanate, based on 100 parts by weight of copolymer, is injected into the extruder. It is best if the extruder is vented so that volatiles produced during the formation of the heat curable polymer can be removed. The devolatilized heat curable polymer can then be further processed in any desired manner. For example, it may be coated onto a wire or cable. The polymer is then cured by heating it to a temperature of at least about 125° C. and more preferably between 150° C. to 315° C.

(2) A second method of making the heat curable polymer is to first react difunctional compound with from 5 to 1000 parts by weight, based on 100 parts by weight of the difunctional compound, of organotitanate at a temperature of from 25° C. to 250° C., more preferably from 100° C. to 200° C. The reaction is preferably carried out in a solvent, such as benzene. Volatile material is then removed from the reaction product. The devolatilized product may be blended with ethylene homopolymer, rubber or any inert polymer, i.e. any polymer that will not react with the reaction product. This blend provides a useful crosslinking agent that may be stored and later mixed with alkylene-alkyl acrylate copolymer.

This second method has the advantage of not requiring further devolatilzation and of avoiding the need to store neat organo titanate, which deteriorates when exposed to atmospheric moisture.

To complete formation of the heat curable polymer, the devolatilized reaction product is blended with alkylene-alkyl acrylate copolymer, in amounts of about 0.1 to about 10 percent by a weight, preferably about 0.5 to about 5 percent by weight, based on the weight of the copolymer. The resultant mixture is heated to temperatures on the order of at least about 125° C., preferably about 150° C. to 315° C. to cure or crosslink the copolymer.

(3) A third method is to blend alkylene-alkyl acrylate copolymer, from 0 to 10 parts by weight, based on 100 parts by weight of copolymer, of difunctional compound and from 0.1 to 10 parts by weight, based on 100 parts by weight of copolymer, of titanium chelate. Upon heating at temperatures previously described, the mixture will cure. However, volatile compounds will evolve, so cure must take place at elevated pressure if void-free product is desired. This method has the advantage of not requiring storage of organo titanates, which deteriorate in atmospheric moisture faster than the titanium chelates.

THE CURED PRODUCT

Upon curing, the product formed has at least the following units:

(a) alpha olefin units having the formula: ##STR17## wherein B is selected from the group consisting of hydrogen, C₁ to C₁₆ alkyl, C₆ to C₁₂ aryl, C₇ to C₁₆ alkaryl or combinations thereof, said alpha olefin units being present in the copolymer to the extent of at least 22 weight percent;

(b) cross-linked bridges of the formula: ##STR18## wherein C₁ is a carbon atom in a polymer chain, and R₂ is a divalent organic radical terminated with other than aryl.

If the preferred difunctional compounds are used, R₂ will comprise: ##STR19## wherein d is an integer of 1 to 4; and

EXAMPLES

The following examples will serve to illustrate the invention.

EXAMPLES 1 TO 4

The ingredients in Table I were blended in a Brabender mixer at a temperature below 125° C.

Each mixture was then pressed into a plaque and subjected to the Monsanto Rheometer cure test. This test procedure is fully set forth in U.S. Pat. No. 4,018,852 issued Apr. 19, 1977, the disclosure of which is incorporated herein by reference. Briefly, FIG. 1 of said patent shows the typical Monsanto Rheometer curve. The cure level (highest cross-link density) is designated as H. It is measured in terms of inch-pounds of torque on the rheometer test equipment. A higher value for H corresonds to a higher cross-link density.

The cured disks from the above test were measured for decalin extractables according to Method A of ASTM D-2765. The decalin insoluble portion of the polyethylene compound is a quantitative measure of its degree of cure. The larger percentage extractables, the lower the degree of cure.

Other specimens were pressed into plaques and cured at 190° C. at 5,000 psig for 15 minutes and tested for tensile strength and elongation under ASTM-D-412-68 and for 60-cycle dielectric constant and dissipation under ASTM-D-150-74. The results appear in Table II.

                  TABLE I                                                          ______________________________________                                                   Amount in Mixture, grams                                             Example No.  1        2        3      4                                        ______________________________________                                         E/EA copolymer.sup.(1)                                                                      198.5    198.5    198.5  198.5                                    Tetraisopropyl                                                                              9.9      5.94     5.94   5.94                                     Titanate (TIPT)                                                                Decanediol   13.9     8.34                                                     Dodecanediol --       --       10.0   10.0                                     Calcined     83       83       83     --                                       Clay filler                                                                    Silica filler                         83                                       Heat Stabilizer.sup.(2)                                                                     1.5      1.5      1.5    1.5                                      ______________________________________                                          .sup.(1) ethylene-ethyl acrylate copolymer containing 18-20 percent ethyl      acrylate, having melt index of 4.5.                                            .sup.(2) flectol H ® available from Vanderbilt Corp, 30 Winfield St.,      Norwalk, Ct. 06855.                                                      

                  TABLE II                                                         ______________________________________                                         Example No.      1       2       3     4                                       ______________________________________                                         H Value           89      72      72    80                                     % Decalin extractables                                                                          4.72    7.66    7.26  5.45                                    Tensile strength (PSI)                                                                          1450    1500    1470  1240                                    Elongation       210     257     250   230                                     Dielectric constant                                                                             3.313   3.256   3.284 3.318                                   Dissipation factor                                                                              0.00306 0.00270 0.00287                                                                              0.0179                                  After Aging 1 week at 121° C.                                           Tensile Strength 1560    1570    1600  1240                                    % Elongation     120     177     190   137                                     ______________________________________                                    

The results tabulated above show that the material was cross-linked and displays properties useful as electrical insulation for wire or cable.

EXAMPLES 5 TO 7

The procedure for Example 1 to 4 was repeated using the ingredients shown in Table III.

                  TABLE III                                                        ______________________________________                                                        Amount in mixture, grams                                        Example No.      5         6       7                                           ______________________________________                                         Copolymer.sup.(1)                                                                               280       198.5   198.5                                       TIPT             13.1      6.2     6.2                                         Difunctional compound.sup.(2)                                                                   12.1       5.75    5.75                                       Talc.sup.(4)     --        83                                                  Treated Clay     --        --      83                                          Heat Stabi1izer.sup.(3)                                                                          1.5      1.5     1.5                                         ______________________________________                                          .sup.(1) same copolymer as Example I.                                          .sup.(2) compound having the formu1a HO--(CH.sub.2)--S--(CH.sub.2).sub.2       --OH                                                                           .sup.(3) same heat stabilizer as Example I.                                    .sup.(4) Mistron ZSC ®, Cyprus Industrial Minerals, Trenton, N.J.    

Results of tests performed on the material are listed in Table IV.

                  TABLE IV                                                         ______________________________________                                         Example No.    5          6       7                                            ______________________________________                                         H Value         65         53      40                                          Tensi1e strength (PSI)                                                                        1410       1640    1630                                         % Elongation   370        440     440                                          ______________________________________                                    

These results show that a cross-linked polymer having suitable physical properties was obtained. Notice in particular the surprisingly high elongation obtained with the particular difunctional compound, HO--(CH₂)₂ --S--(CH₂)--₂ --OH, used in Examples 5, 6 AND 7.

EXAMPLES 8 AND 9

The procedure for Examples 1 to 4 as repeated using the ingredients shown in Table V.

                  TABLE V                                                          ______________________________________                                                         Amount in Mixture, grams                                       Example No.       8       9                                                    ______________________________________                                         Copolymer.sup.(1) 265     265                                                  TIPT              7.3     4.9                                                  Decanediol        9.75    6.5                                                  Heat Stabilizer.sup.(2)                                                                          1.5     1.5                                                  ______________________________________                                          .sup.(1) Ethylene-ethyl acrylate copolymer containing 2 weight % ethyl         acrylate having melt index of 2.                                               .sup.(2) Same heat stabilizer as Example 1.                              

The material exhibited the properties shown in Table VI.

                  TABLE VI                                                         ______________________________________                                         Example No.          8      9                                                  ______________________________________                                         Tensile strength (PSI)                                                                              2210   2060                                               % Elongation          600    585                                               % Decalin extractables.sup.(1)                                                                      24.76  27.76                                              ______________________________________                                          .sup.(1) After curing at 182° C.                                  

The results listed in Table VI show that a cross-linkable polymer is obtained with ethylene-ethyl acrylate copolymer containing only 2% ethyl actylate.

EXAMPLES 10 TO 14

These examples illustrate the invention using various difunctional compounds, namely, 1,5 pentanediol, 1,5 pentanediol diacetate, 2,5 hexanediol, 1,4 butanediol diadipate, and cyclohexane dimethanol having the formula ##STR21## The procedure for Examples 1 to 4 was followed with the ingredients listed in Table VII.

                  TABLE VII                                                        ______________________________________                                                   Amount in Mixture, grams                                             Example No. 10       11     12     13   14                                     ______________________________________                                         Copolymer.sup.(1)                                                                          45       45     45     45   45                                     1,5 Pentanediol                                                                            1.45                                                               1,5 Pentanediol      2.62                                                      diacetate                                                                      2,5 Hexanediol              1.6                                                1,4 Butanediol                     4.4                                         diadipate                                                                      Cyclohexane                             2.0                                    dimethanol                                                                     TIPT        1.7      1.7    1.7    1.7  0.95                                   ______________________________________                                          .sup.(1) Same copolymer as for Example I.                                

These materials exhibited the results listed in Table VIII.

                  TABLE VIII                                                       ______________________________________                                         Example No.                                                                               10     11       12     13   14                                      ______________________________________                                         H Value    36     61       8      8    18                                      % Decalin  18.26  11.32    49.11  58.06                                                                               37.5                                    extractables                                                                   ______________________________________                                    

Examples 10 to 14 show that a cross-linked polymer was obtained in all cases.

EXAMPLES 15 TO 18

These examples illustrate practice of the invention using yet another group of difunctional compounds, specifically ethylene glycol, ethylene glycol diacetate, and a brominated diol. The procedure for Examples 1 to 4 was followed with the ingredients in Table IX except as noted.

                  TABLE IX                                                         ______________________________________                                                      Amount in mixture, grams                                          Example No.    15     16       17    18                                        ______________________________________                                         Copolymer.sup.(1)                                                                             45     45                                                       Copolymer.sup.(2)              256.6                                           Copolymer Compound.sup.(5)           254.4                                     Ethylene glycol                                                                               0.5                                                             Ethylene glycol       1.2                                                      diacetate                                                                      Brominated diol.sup.(4)        35.8  25.5                                      TIPT           1.0    1.0      7.0   6.6                                       Heat stabilizer.sup.(3)        1.6   1.5                                       Filler.sup.(6)                 15.8  12                                        ______________________________________                                          .sup.(1) Same copolymer as Example 1.                                          .sup.(2) Ethyleneethyl acrylate copolymer containing 15-17 weight percent      ethyl acrylate, having melt index of 1                                         .sup.(3) Same heat stabilizer as for Example 1.                                .sup.(4) Compound having the formula:                                          ##STR22##                                                                      sold under the trade name BA50 by Great Lakes Chemical Corp. Lafayette,        Indiana.                                                                       .sup.(5) Talc filled polyethylene copolymer containing the cocopolymer of      foot note .sup.(2)  sold under the trade name DFNA6989 by Union Carbide        Corporation, Old Ridgebury Rd. Danbury, Ct.                                    .sup.(6) Superpflex 200 ®, sold by Pfizer Corp., Easton, Pa.         

These materials exhibited the results listed in Table X.

                  TABLE X                                                          ______________________________________                                         Example No.    15     16        17   18                                        ______________________________________                                         H value        13.sup.(1)                                                                            13.sup.(1)                                                                               --   --                                        Tensile strength                                                                              --     --        2560 1540                                      (psi)                                                                          % Elongation   --     --         613  347                                      % Deformation.sup.(2)                                                                         --     --        68.5 43.4                                      at 121° C.                                                              ______________________________________                                          .sup.(1) plaque cured at 500° F. before rheometer test,                 .sup.(2) ASTM-D-621                                                      

The results listed in Table X show that a cross-linked copolymer was obtained. It is believed that the brominated difunctional compound of Examples 17 and 18 imparts flame retardancy to those polymers.

EXAMPLES 19 AND 20

Thus far, the examples have shown the embodiment of the invention wherein the copolymer, difunctional compound, and titanate are all mixed and heated to form a heat curable polymer. Examples 19 and 20 illustrate the embodiment of the invention wherein the difunctional compound is prereacted with the titanate, prior to mixing with copolymers.

Five hundred cc of benzene were heated and 55 cc were boiled away to assure dryness. Decanediol (112 g.) was dissolved in the remaining hot benzene and 80. g of TIPT diluted with 84 cc benzene were added to the benzene-decanediol mixture dropwise over a period of 1/2 hour. A reaction took place, evidenced by the liberation of heat and build-up of a glassy substance on the bottom of the reactor. The benzene was boiled away and the material, i.e. the TIPT-decanediol adduct, was collected and pulverized. The adduct was mixed with copolymer and other ingredients in the amounts listed in Table XI.

                  TABLE XI                                                         ______________________________________                                                         Amount in Mixture, grams                                       Example No.       19      20                                                   ______________________________________                                         Copolymer.sup.(1) 198.5                                                        Copolymer.sup.(2)         265                                                  Adduct             17.3   13                                                   Talc.sup.(4)      83                                                           Heat Stabilizer.sup.(3)                                                                           1.5    1.5                                                  ______________________________________                                          .sup.(1) Same copolymer as in Example 1.                                       .sup.(2) Same copolymer as in Example 8.                                       .sup.(3) Same heat stabilizer as in Example 1.                                 .sup.(4) Same filler as Example 6.                                       

The results of testing the compounds are shown in Table XII.

                  TABLE XII                                                        ______________________________________                                         Example No.        19       20                                                 ______________________________________                                         H valve             65       8                                                 Tensile strength   1380     1580                                               (psi)                                                                          % Elongation        200     595                                                % Decaline extractable                                                                            2.90      36                                                ______________________________________                                    

The results listed in Table XII shows that a cross-linked polymer was obtained in both cases.

EXAMPLE 21 TO 24

These examples illustrate the embodiment of the invention in which titanium chelate are used. The mixing and testing procedure are the same as those of Example 1.

                  TABLE XIII                                                       ______________________________________                                                       Amount in Mixture, grams                                         Example No.     21     22        23   24                                       ______________________________________                                         Copolymer.sup.(1)                                                                              48     48        48   48                                       Titanium Acetyl 3.4                                                            Acetonate                                                                      Triethanolamine        4.1                                                     Titanium chelate                                                               Tetraoctylene glycol             4.3                                           Titanium chelate                                                               Lactic acid titanium                  2.4                                      chelate                                                                        Decanediol      2.8    2.8       2.8  2.8                                      ______________________________________                                          .sup.(1) Same copolymer as Example 1.                                    

The compounds were tested. The results are listed in Table XIV.

                  TABLE XIV                                                        ______________________________________                                         Example No.  21.sup.(1)                                                                            22.sup.(1) 23.sup.(2)                                                                          24.sup.(1)                                 ______________________________________                                         H-Valve      86     86         65   95                                         % decalin    6.62   8.18       7.88 4.15                                       extractable                                                                    ______________________________________                                          .sup.(1) Compound was pressed and cured at 500° F.                      .sup.(2) Compound was pressed and cured at 600° F.                

The data in Table XIV indicate that a cross-linked polymer was obtained in Examples 21 to 24.

EXAMPLES 25 TO 27

In Example 25, the diol, i.e. the difunctional compound, was generated in situ by the chelate. In Example 26, the chelate was generated in situ from TIPT and triethanolamine, forming triethanolamine titanium chelate. In Example 27, the tetraoctylene glycol titanium chelate was formed in situ from 2-ethyl-1,3-hexane diol and TIPT.

                  TABLE XV                                                         ______________________________________                                                      Amount in Mixture, grams                                          Example        25          26      27                                          ______________________________________                                         Copolymer.sup.(1)                                                                             338         338                                                 Copolymer.sup.(2)                  250                                         2-ethyl-1,3-hexanediol             23.24                                       Titanium chelate                                                                              .sup.  16.2.sup.(3)                                             Decanediol                 10.5                                                TIPT                        7.6    11.31                                       Triethanol amine           7.83                                                Heat Stabilizer.sup.(4)                                                                       1.7          1.7    1.5                                         ______________________________________                                          .sup.(1) Same copolymer as Examp1e 1.                                          .sup.(2) Ethylene-ethyl acrylate copolymer containing 14% ethyl acrylate,      having melt index of 2.0.                                                      .sup.(3) Same chelate as Example 23.                                           .sup.(4) Same heat stabilizer as Example 1.                              

The results of testing the compound after curing at high temperatures are listed in Table VI.

    ______________________________________                                         Example    25.sup.(1)    26.sup.(1)                                                                            27.sup.(1)                                     ______________________________________                                         H valves   17.5          77     11.2                                           % Decalin  24.2          7.52   30.8                                           extractables                                                                   ______________________________________                                          .sup.(1) Cured at 600° F.                                               .sup.(2) Cured at 500° F.                                         

The results show that in Examples 25 to 27, all performed in accordance with the invention, a cross-linked polymer was obtained. 

What is claimed is:
 1. A cross-linking agent, suitable for cross-linking an alkylene-alkyl acrylate copolymer to a cross-linked product, which is the reaction product of a mixture containing a difunctional compound which can be 1,5-pentanediol diacetate, a compound having the formula HO--CH₂ --CH₂ --S--CH₂ --CH₂ --OH, or a compound falling within the scope of the formula HO--CH₂ --OH selected from the group consisting of decanediol and dodecanediol; and from 5 to 100 parts by weight, based on 100 parts by weight of the dihydroxy compound, of an organo titanate.
 2. A cross-linking agent as defined in claim 1 wherein the organo titanate is selected from the group consisting of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraoctyl titanate, tetrastearyl titanate, isopropyl tri)lauryl-myristyl) titanate and combinations thereof.
 3. A cross-linking agent as defined in claim 1 wherein the difunctional compound is decanediol and the organo titanate is tetraisopropyl titanate.
 4. A cross-linking agent as defined in claim 1 in admixture with an inert polymer.
 5. A cross-linking agent as defined in claim 1 wherein the difunctional compound has the formula:

    HO--CH.sub.2 --CH.sub.2 --S--CH.sub.2 --CH.sub.2 --OH


6. A cross-linking agent as defined in claim 1 wherein the difunctional compound is a decanediol.
 7. A cross-linking agent as defined in claim 1 wherein the organo titanate is tetraisopropyl titanate.
 8. A cross-linking agent as defined in claim 2 wherein the organo titanate is tetraisopropyl titanate.
 9. A cross-linking agent as defined in claim 2 wherein the difunctional compound is decanediol and the organo titanate is tetraisopropyl titanate.
 10. A cross-linking agent as defined in claim 2 wherein the difunctional compound is dodecanediol and the organo titanate is tetraisopropyl titanate.
 11. A cross-linking agent as defined in claim 1 wherein the difunctional compound is 1,5-pentanediol diacetate and the organo titanate is tetraisopropyl titanate.
 12. A cross-linking agent as defined in claim 1 wherein the difunctional compound has the formula HO--CH₂ --CH₂ --S--CH₂ --CH₂ --OH and the organo titanate is tetraisopropyl titanate.
 13. A cross-linking agent as defined in claim 1 wherein the organo titanate is selected from the group consisting of titanium acetyl acetonate, triethanol titanium chelate, tetraotylene glycol titanium chelate and the lactic acid titanium chelate.
 14. A cross-linking agent as defined in claim 13 wherein the difunctional compound is decanediol.
 15. A cross-linking agent as defined in claim 7 wherein the difunctional compound is decanediol.
 16. A cross-linking agent as defined in claim 7 wherein the difunctional compound is dodecanediol.
 17. A cross-linking agent as defined in claim 7 wherein the difunctional compound is 1,5-pentanediol diacetate.
 18. A cross-linking agent as defined in claim 7 wherein the difunctional compound has the formula HO--CH₂ --CH₂ --CH₂ --S--CH₂ --OH. 